Accidental and intentional overdose with prescription and over the counter drugs is a serious health problem with thousands of fatalities occurring each year as a result. The present invention relates to pharmaceutical compositions comprised of a chemical moiety attached to an active agent in a manner that substantially decreases the potential of the active agent to cause overdose or to be abused. When delivered at the proper dosage the pharmaceutical composition provides therapeutic activity similar to that of the parent active agent. However, when the composition is delivered at higher doses the potential for overdose or abuse is reduced due to the limited bioavailability of the active agent as compared to the active agent delivered as free drug.